The present invention relates to a process for edge-machining an optical lens.
In particular, the invention relates to a process for edge-machining spectacle lenses, which allows spectacle lenses to be finished at the edge with the necessary precision in very short machining times.
Where the term spectacle lenses is used below, it should be understood to mean optical lenses or lens blanks for spectacles made of the usual materials, i.e. inorganic glass or plastics, such as polycarbonate, CR-39, HI-Index etc., and with circumferential edges of any shape, which lenses or lens blanks may be, but do not have to be, machined on one or both optically effective surfaces prior to machining of the edge thereof.
The purpose of spectacle lens edge machining is to machine the edge of a spectacle lens so that it is ready for insertion into a spectacle frame. To this end, the spectacle lens is on the one hand provided, when viewed in plan, with a circumferential contour which is substantially complementary to the circumferential contour of the holder, i.e. the circumferential contour of the spectacle frame. On the other hand it may be necessary, depending on the type of holder, to form a groove or bevel at the spectacle lens edge, which serves for form-fitting securing of the spectacle lens to the spectacle frame. To ensure that the spectacle lens fits into the spectacle frame after edge-machining, or to be able to determine the position of the groove or bevel on the spectacle lens edge, the edge of the spectacle lens is measured after a preliminary machining stage, which is generally performed with cooling liquid feed, and then finish-machined taking account of the measured edge data, optionally with formation of the groove or bevel.
DE-A-38 27 122 discloses a process for edge-machining a spectacle lens, which comprises the following stages:
preliminary machining of an edge of the spectacle lens rotatable in an angularly controlled manner about a rotational axis of a workpiece by means of a first edge-machining tool adjustable radially relative to the rotational axis of the workpiece, wherein the spectacle lens is provided with a circumferential contour which corresponds to the circumferential contour of a holder for the spectacle lens apart from a slight degree of oversizing,
contactless measurement of the edge of the preliminarily machined spectacle lens and
finish-machining of the edge of the spectacle lens, taking account of the detected edge data of the preliminarily machined spectacle lens, by means of a second edge-machining tool adjustable radially relative to the rotational axis of the workpiece, wherein the spectacle lens is provided with a circumferential contour substantially complementary to the circumferential contour of the holder.
Although this edge-machining process exhibits advantages in comparison to other previously known processes (e.g. EP-A-0 160 985), in which the edge data of the preliminarily machined spectacle lens are mechanically scanned to obtain information for finishing of the spectacle lens edge, said advantages being to the effect that, due to the contactless measuring arrangement, damage to the spectacle lens/measuring arrangement and/or movements or deformation thereof during measurement which might falsify the measuring results are prevented, a disadvantage of this prior art is in particular that it did not always prove possible to detect reliably or within acceptable time limits the edge data of the preliminarily machined spectacle lens using the measurement principles described in DE-A-38 27 122. Further measurement arrangements, which use a VCR-System or a Laser-Scanning-System for contactless scanning of the edge of a machined spectacle lens, are known from DE-A-198 04 542 and DE-A-197 02 287, respectively.
In relation to the above prior art, the object of the invention is to provide a process for edge-machining optical lenses which is improved in particular with regard to machining speed and precision.
According to the present invention, there is provided a method of edge-machining an edge of an optical lens, in particular a spectacle lens, which is rotatable in an angularly controlled manner about a rotational axis of a workpiece to form the lens, the method comprising the steps:
preliminary machining of the edge of the lens by means of a first edge-machining tool that is adjustable at least radially relative to the rotational axis of the workpiece, wherein the lens is provided with a circumferential contour which corresponds to a circumferential contour of a holder for the lens apart from a slight degree of oversizing,
contactless measurement of the edge of the preliminarily machined lens, and
finish-machining of the edge of the lens, taking account of the detected edge data for the preliminarily machined lens, by means of a second edge-machining tool that is adjustable at least radially relative to the rotational axis of the workpiece, wherein the lens is provided with a circumferential contour substantially complementary to the circumferential contour of the holder,
wherein, during preliminary machining of the edge of the lens, a surface which is definedly matt in the dry state is produced at the edge,
wherein, if preliminary machining of the edge of the lens is performed with cooling liquid supply, at least the edge of the preliminarily machined lens is dried before the edge is measured, and
wherein, to measure the edge, a bundle of laser beams is directed towards the dry, definedly matt surface of the edge by means of a laser in a predetermined positional relationship to the rotational axis of the workpiece, and an image of the point of impact of the laser beams is recorded by means of a video camera in a predetermined positional relationship to the rotational axis of the workpiece, wherein the recorded image is then evaluated with respect to a distance of the point of impact from the rotational axis of the workpiece, in order to determine the edge data of the preliminarily machined lens.
The basis for the invention is the idea that it would be particularly desirable, in order to accelerate the edge-machining of lenses, to reduce the nonproductive times, i.e. the times during which no shaping machining occurs between the respective edge-machining tool and the lens edge. In this respect, it has emerged that, due to the procedure according to the invention, which is fundamentally geared to measuring the dry or dried, definedly matt surface of the edge of the preliminarily machined lens by means of a measuring arrangement consisting of laser and video camera and operating in a particular way without contact, the edge data of the preliminarily machined lens may be determined with increased accuracy markedly more quickly than was previously possible, such that the nonproductive times required therefor may be reduced considerably relative to the prior art.